This invention relates to a reversible D.C. motor with a permanent magnet rotor and electronic commutating device, in general and more particularly to improved arrangement for controlling, such a motor.
Reversible D.C. motors of this type in which the polarity of the desired speed voltage of a speed control device and the commutating sequence of the commutating transistors which reverse a motor voltage specified by the speed control device applied to the stator windings for reversing the direction of rotation after the delivery of a direction of rotation signal, initiated by the speed control device, to a selection circuit are known.
In motors of this type, the actual speed value cannot be obtained, off hand, from the EMF induced in the stator windings by the permanent magnet rotor. It is known to take this EMF off by means of diodes. However, the EMF coupled out in this manner is proportional only to the absolute amount of the speed value. It is for this reason that the coupling out of the EMF by means of diodes can be applied only within limits.
The direction of rotation of brushless D.C. motors is reversed, not by a reversal of polarity of the supply voltage, but by the reversal of the sequence in which the stator windings are energized. Therefore, regardless of the direction of rotation of the permanent magnet rotor, the direction of the motor current is always the same, thus obtaining an EMF dependent on the direction of rotation is not possible, off hand, in brushless motors reversible in their direction of rotation.